The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor.
Nondestructive inspection (xe2x80x9cNDIxe2x80x9d) is a field which includes all means of evaluating the quality and strength of materials and structures without adversely affecting their quality, strength or usefulness. NDI usually includes methods recognized by the American Society of Nondestructive Testing (xe2x80x9cASNTxe2x80x9d). These methods include, but without limitation, radiography, eddy current testing, dye penetrant testing, ultrasonic testing, leak testing, thermography, and the like. These methods help find cracks, corrosion, weld flaws, rolling or processing flaws, thickness variations and various other imperfections or discontinuities that may affect quality and strength of a material or structure.
Detection and discrimination of the type of imperfections or discontinuities on the interior or inside surface of a tubular shape is difficult even with all the presently available testing when only the exterior is accessible. Even ultrasonic inspection with a single crystal search unit does not clearly indicate the type of discontinuity or imperfection.
A method that can be utilized to inspect the inner surface of a tubular shape is real time imaging of ultrasound waves. Real time imaging of ultrasound waves can utilize a modified Charge Coupled Device (xe2x80x9cCCDxe2x80x9d) camera. Any other device capable of imaging ultrasound waves or beams may also be utilized. The camera provides images with normal television framing rates of 100% of the interior parts. The method utilizes high frequency sound waves or beams (ultrasound) instead of ionizing radiation. Sound beams are passed through the test piece (the tubular shape) being inspected and are partially attenuated by discontinuities and imperfections. The internal volume of the test piece is therefore imaged as in radiography (volumetric inspection). This then provides a shadowgraph display similar to a real time X-ray except that no ionizing radiation is present. Unlike radiographic (X-ray) methods, sound waves are strongly blocked by cracks, voids and other interfacial discontinuities. This provides higher sensitivity to critical and potentially dangerous discontinuities or imperfections.
The real time imaging of ultrasonic waves or beams typically utilizes one of three methods. The first method passes the sound beam entirely through the test piece, material or structure (through transmission). The second method introduces the sound beam from the front of the test piece (perpendicular to it) and then images the part of the beam reflected back to the camera. The third method introduces the sound beam into the test piece at an angle so that the reflection from a surface of the test piece (a specular reflection) is imaged by the camera (or a camera chip). The difficulties preventing the present art from accomplishing the imaging of the inner surface of a tubular shape is the scatter of the ultrasonic beam by the curved pipe surfaces and the relatively strong reflection from the outer surface, which obscures the weaker reflection from the inner surface of the tubular shape. Thus there exists the need for a method or apparatus that may be used to inspect a tubular shape, particularly, to inspect the inner surface of a tubular shape and may be used when only the outside or exterior surface of the tubular shape is accessible.
For the foregoing reasons, there is a need for a new method for acoustic imaging of a tubular shape that can quickly inspect the inner or interior surface and outer or exterior surface of a tubular shape and discern small discontinuities before they can cause failure.
The instant invention is directed to a method for acoustic imaging of a tubular shape that satisfies the needs enumerated above and below.
The present invention is directed to a technique for the inspection of a tubular shape or a tubular test piece of various wall thickness. A tubular shape is, but without limitation, typically defined as a hollow cylinder, and typically used for conveyance of a fluid (gas or liquid). A tubular shape may also be a cylinder or drum with closed ends used for liquid or gas storage. A tubular shape may also be referred to, but without limitation, as a tubular product, tubing, a conduit, a pipe, piping, a channel, a tube, a hollowed beam, a fluid conveyor, or a hose. Typically tubular shapes are manufactured from metals, metal alloys, rubber, ceramics, plastics, polyvinyl chloride (PVC), or any type of material that lends itself to storing, conveying, or transporting fluids.
The present invention utilizes real time ultrasonic imaging in a new and unique way. The ultrasonic sound beam is initiated by an ultrasonic transducer and directed through a focusing lens of unique design to redirect the beam through the outer surface of the tubular shape and into the tubular shape wall. The ultrasonic beam is then reflected at the inner surface of the tubular shape, passes back through the outer surface of the tubular shape, through the same or another focusing lens in the opposite direction and to an imaging camera chip separate from and lying more or less beside the initiating transducer. The imaging camera chip then converts the ultrasonic beam into an image of the inner surface, the outer surface and an internal volume image of the tubular shape.
There are two primary methods to direct the beam to and through the tubular shape. The first method utilizes an angle beam arrangement. In the angle beam arrangement, the beam is directed through the outer surface of the tubular shape and into the tubular shape, not perpendicular to the outer surface, but at an oblique angle to the outer surface or at an oblique angle to a line drawn vertical to the outer surface of the tubular shape.
A second method utilizes the same focusing lens design but utilizes a beam splitter arrangement. In this method the sound beam is directed through the lens along a line perpendicular to the surface of the tubular shape or perpendicular to a line drawn vertical to the outer surface of the tubular shape. The sound beam passes through the outer surface of the tubular shape and changes direction by refraction (refraction is defined, but without limitation, as a change of direction of rays, beams, or waves which are obliquely incident upon and pass through a surface bounding two media in which the ray, beam or wave has different velocities.) The sound beam passes from the outer surface to the inner surface and reflects from the inner surface. It passes through the tubular shape wall and again through the outer surface, being refracted there. It then passes back through the focusing lens and to the imaging camera chip. The beam in this instance strikes the inner surface at a 90-degree angle. In both methods, the reflection from the outer surface and the inner surface are both imaged but can in many instances be separated electronically by range gating.
It is an object of the invention to provide a method for acoustic imaging of a tubular shape that is a nondestructive inspection technique.
It is an object of the invention to provide a method for fast inspection of the inner (interior) surface of a tubular shape when the tubular shape is either empty or full of fluid.
It is an object of the invention to provide a method for acoustic imaging a tubular shape that may be used to inspect the inner and outer surface of a tubular shape when only the outside surface is accessible.